I live in Florida, so I generally only have two suits, a "cold weather" (3/2 full) and just a 1.5mm longsleeve wetsuit top for when it's just a little chilly to go with nothing.

Unfortunately the top is falling apart after only a year, so I need to decide to replace it or if I want something else. I was thinking about getting a 2mm shortsleeve shorty, but I've never worn one and am not sure exactly how warm it would be compared to the top.

Have a look at the Mystic metalite top, it's a 1.5m top but is rediculously warm.
I wear one with board shorts. If its cold I have a mystic long sleeve short leg wetsuit.
King of water sports usually has good prices, also the new oneil gear looks good.

Unfortunately the top is falling apart after only a year, so I need
...

Was that Top a cheaply-made product , or do you think it was the way
you put it on ; if Ya think it was just a cheap brand, then what was the
name so the rest of us can stay away.

Those spandex biking shirts work Really well as an under garment to
stay Way warmer, even with a shorty , then Ya got the option to not use
it if it's too warm; also keeps the long-sleeve tops from stretching out when
you put it on. I was Good at destroying tops till someone told me about spandex.

After about 8 months or so, I noticed the back would stick together, and as I stretched it to put it on the neoprene would stick together and tear. I didn't realize what was happening until it was pretty bad. It's all across the back and on the arms as well. Two of my friends haven't had issues with theirs but have only had them a few months ... I may have gotten unlucky with leaving it in the sun or something. Other than that I really liked it, super warm for what it is.